Hi Chris, now would be the best time to apply a pre emergent crab grass control. You can buy it at Home Depot and it's really a post and pre emergent. I find the Scotts brand works the best. I use it every spring as my first fertilizer, it not only kills any crab grass seeds but it also gets your lawn going and looking great.......Wayne

Just a hint for years to come. I live in z4, and have heard a number of horticulturists say to watch the lilac bushes. It's mother nature's way of telling you it is time to put down your crabgrass killer. The time is right when you start to see color on the lilac buds. NOT when they open, but, when you start to see color from the buds.

While I think that the absolute last thing Mother Nature wants to tell me is to put down herbicides, I seem to have managed to get the timing right. (zone 5).
I put some pre-emergent down along the edges and applied CGM to the lawn itself and, so far, no sign of the evil crab grass. So far so good!

Can one get CGM at Home Depot? How to apply it. I know it is too late to do it now (I already have the crab grass everywhere), but for future use. However, is there anything I can do to get rid of it once it appears? It has not any seeds yet and I'l like to kill it before that happens.

Last year, the crabgrass pretty much took over a 15x12 foot section of my front lawn. The crabgrass moved in after that section got churned up by a skunk looking for grubs - crabgrass tends to take hold in disturbed soil.

I didn't want to use herbicides, especially since I applied nematodes to deal with the grubs. So I waited until the crabgrass was of a size to handle easily and then got on my hands and feet and yanked it all out by the roots.
When I was done the entire section was pretty much all open soil, with very little grass surviving. I overseeded and the grass came in very nicely.

However, I had no illusions that there were a million seeds in there, which is what prompted my post.

This spring, then, I did use the pre-emergent and CGM. I wish they didn't feel that they have to add fertilizer to the preemergent but that's all I could find. I used CGM to further suppress germination but also to try to even out the areas that didn't get pre-emergent/fertilizer. I still ended up with some patches but that's sorted itself out by now.

So far, I've not seen any crabgrass in the lawn and the area that I've reseeded looks absolutely wonderful. In fact, it's come in so thick that I've had a bit of a chore trying to mow it with my reel mower. Time to sharpen those blades! :)

I have to agree with the Forsythia plan. I had a landscaper that told me that he always used the Forsythia as a guide to when the right time to spread the pre emergence crabgrass preventer. The trick is to get it down before the seeds germinate and that has to do with temperature of the soil. Every year that can be different, so it you wait till the Forsythia start to bloom as a guide you are pretty sure of being on time with the application. Of course it needs to be watered in as well, so if you don't get rain soon after that you might need to water it in a bit.